Dazzling Red-Emitting Europium(III) Ion-Doped Ca2LaHf2Al3O12 Garnet-Type Phosphor Materials with Potential Application in Solid-State White Lighting

Lanthanide-dependent photoluminescence and thin film fabrication of host CaWO4 micro-materials for potential indoor plant growth applications

A set of scheelite (CaWO4, CWO) doped samples with formula Ca1-2xLnxNaxWO4 (x = 0 and 0.1; Ln = Eu, Tb and Gd) (Eu@CWO, Tb@CWO and Gd@CWO) and doped phases with combinations LnxLn'y = Eu0.05Tb0.05, Eu0.05Gd0.05, Tb0.05Gd0.05 (Eu,Tb@CWO, Eu,Gd@CWO and Tb,Gd@CWO) and Eu0.033Tb0.033Gd0.033 (Eu,Tb,Gd@CWO) were prepared by a modified four-step sol-gel method followed by calcination at mild temperatures. The solids were characterized by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). An in-depth analysis of the structure and the impact of the synthesis approach on crystallite shape and size was carried out using Rietveld refinements. Besides, the solid-state photoluminescence was studied in terms of excitation, emission 4f-4f* transitions, lifetimes (τobs), radiative and non-radiative constants (kr and knrad), energy transfer migration analysis and europium quantum yields. Finally, the Eu-containing CWO samples were selected as a potential emitter device constructed using a spin-coating technique giving rise to homogeneous coatings onto square glass substrates. These results are promising for the design and construction of devices based on wolframate micro-sized materials with emission properties and potential applications in plant cultivation LEDs, sensing, photocatalysis and solar cells.

Improving Thermal Stability of Eu3+ Luminescence via High-Concentration Terbium Doping in NaGd2Ga3Ge2O12 Garnet

Phosphors for white light-emitting diodes (WLEDs) would suffer from inadequate luminescent thermal stability, especially at high temperatures, affecting both the reliability and lifespan of devices. Thus, the development of phosphors with excellent thermal stability is a crucial task. By use of a high-temperature solid-state reaction method, a series of Tb3+ and Eu3+ codoped NaGd2Ga3Ge2O12 (abbreviated as NGGGO) phosphors has been successfully synthesized. With an appropriate doping concentration of Tb3+ and Eu3+, the NGGGO:Tb3+,Eu3+ phosphors can provide color tunable emissions; simultaneously, the energy transfer (ET) efficiency from Tb3+ to Eu3+ can reach nearly 100%. Notably, high-concentration Tb3+ doping in NGGGO could induce oxygen vacancies, giving significant enhancement on the thermal stability of Eu3+ luminescence. For the NGGGO:60% Tb3+,1.6% Eu3+ phosphor, the emission intensity of Eu3+ at 450 K remained even higher than that observed under room-temperature conditions. By use of the as-synthesized phosphor as a red emission converter, a near-ultraviolet pumped WLED device can be fabricated. Under a driving current of 20 mA, the device exhibits high color rendering index (CRI) ∼ 89, low correlated color temperature (CCT) ∼ 4603 K, and bright white light with CIE chromaticity coordinates of (0.3569, 0.3587), which demonstrates the potential of NGGGO:Tb3+,Eu3+ phosphors in WLED application.

Synergetic Contributions of High Quenching Concentration and Tuned Square Antiprism Geometry Boosting Far-Red Emission of Eu3+ with Near-Unit Efficiency

Far-red phosphors have emerged as a desirable research hotspot owing to their critical role in promoting plant growth. Especially, Eu3+ ions typically present the 5D0→7FJ (J = 0, 1, 2, 3, 4) transitions, which overlap with the far-red light required for plant photosynthesis. However, achieving high-efficiency far-red emission of Eu3+ remains challenging due to weak 5D0→7F4 transition and concentration quenching. The study constructs two anomalously efficient far-red garnet phosphors A3Sc2C3O12 (A = Y3+, Gd3+. C = Al3+, Ga3+):Eu3+. A high-resolution STEM measurement equipped with an aberration corrector provides the direct proofs for both the [EuO8] configuration-dependent strong 5D0→7F4 and the origin of high quenching concentration. Excitedly, a two-component substitution (replacing Y3+-Al3+ with Gd3+-Ga3+) triggers a near-unity internal quantum efficiency (IQE = 99.01%) and high external quantum efficiency (EQE = 38.73%) in Gd3Sc2Ga3O12:60%Eu3+, resulting from the effective modulation of 5D0→7F4/7F2 transitions. A far-red LEDs device based on Gd3Sc2Ga3O12:60%Eu3+ exhibits an output power of 113 mW at 300 mA. Subsequently, practical applications for promoting plant growth underscore the significance of these findings. This work opens a new path for the development of highly efficient far-red phosphors via the synergistic effect of Eu3+ square antiprism configuration and high quenching concentration.

Investigation to Understand the Role of Phase Variation in Red Emitting Eu3+-Doped Calcium Magnesium Silicate Phosphor for In Vitro Bioimaging

Eu3+-doped silicate phosphors are gaining significant attention for bioimaging and scaffold development due to their narrow red emission, high color purity, quantum yield (QY), and large Stokes shift. These phosphors offer several advantages over conventional imaging techniques, such as good selectivity and sensitivity, simpler operation, reduced data acquisition time, cost-effectiveness, and nondestructive imaging. The luminescence properties of these phosphors can be enhanced by modifying synthesis methods, annealing conditions, and hosts and introducing multiple dopants. This study explores a novel approach for improving luminescence by modifying the crystal structures of Eu3+ doped calcium magnesium silicate (CMS:Eu3+) phosphors for in vitro bioimaging and potential scaffold development. The synthesized diopside (CaMgSi2O6:xEu3+; x = 10, 15, and 20 mol %), merwinite (Ca3MgSi2O8:15 mol % Eu3+), and akermanite (Ca2MgSi2O7:15 mol % Eu3+) phases of CMS:Eu3+ exhibit distinct coordination environments for Eu3+, leading to unique excitation wavelength tunability from ultraviolet (UV) to the visible region, high emission intensity, decay time, QY > 40%, and color purity >83%. A comparative analysis of their structural and photoluminescence properties reveals the impact of phase modifications on luminescence for in vitro bioimaging by optimizing the dopant concentration. The results indicate that CaMgSi2O6: 15 mol % Eu3+ is the most efficient phosphor for in vitro bioimaging, with the highest relative emission intensity in the red region, decay time ∼2 ms, QY ∼ 77%, and color purity ∼86%. The unique morphology of Ca3MgSi2O8:15 mol %Eu3+ and Ca2MgSi2O7:15 mol % Eu3+ also supports cell adhesion, suggesting their potential in scaffold development. In brief, the study highlights the potential of CMS:Eu3+ phosphors for in vitro bioimaging and scaffold development by modifying phases and dopant concentrations.

Eu3+ singly-doped and Eu3+/Sm3+ co-doped ZnS quantum dots: structure, optical properties and energy transfer

In this study, Eu3+ ion singly doped and Eu3+/Sm3+ ions co-doped ZnS semiconductor quantum dots (QDs) were successfully synthesized using a wet chemical method in 1-octadecene (ODE) solvent. The successful doping of Sm3+ and Eu3+ ions into the ZnS host lattice and the composition and valence of the elements present in the sample were confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Structural and morphological studies revealed the presence of Eu3+-doped ZnS and Eu3+/Sm3+ co-doped ZnS QDs of about 3-4 nm size with a zinc blende structure. The Judd-Ofelt (J-O) intensity parameters of Eu3+-doped ZnS QDs were determined from their fluorescence spectra. The optical properties of Eu3+/Sm3+ co-doped ZnS QDs were studied by changing the Eu3+ ion concentration and fixing the Sm3+ ion concentration. The photoluminescence (PL) spectra of Eu3+/Sm3+ co-doped ZnS QDs were obtained at an excitation wavelength of 403 nm (6H5/2 → 6P3/2 transition of Sm3+ ions) in the 525-725 nm range. The effective energy transfer (ET) process from Sm3+ to Eu3+ ions was confirmed and explained in detail using the Reisfeld approximation and the Inokuti-Hirayama model. The CIE color coordinates of the Eu3+/Sm3+ co-doped ZnS QDs were obtained using PL spectral data. Eu3+/Sm3+ co-doped ZnS QDs exhibited a long lifetime and emitted warm red light. These interesting properties give Eu3+/Sm3+ co-doped ZnS QDs great potential for applications in photovoltaics, photocatalysis, and biomarkers.

Excellent luminescent thermal stability of Dy3+/Sm3+ co-activated multifunctional titanate single-phase phosphors

Nowadays, the development of phosphors with excellent luminescent thermal stability for various applications has become a research hotspot. Therefore, the Dy3+/Sm3+ co-activated multifunctional NaYTiO4 phosphors with excellent comprehensive performance in the field of non-contact optical measurement and white LED solid-state lighting were reported in this paper, and their crystal structure, elemental composition, optical bandgap and photoluminescence properties were systematically studied. Remarkably, the reason why NaYTiO4:Dy3+,Sm3+ phosphors achieved color-controlled emission from yellow to orange-red and even to white at the excitation wavelength of 363 nm was not based on the energy transfer process from Dy3+ to Sm3+ but on co-excitation. When the temperature reached 475 K, the luminescence intensity of the phosphor still maintained 96.75% of the initial intensity, demonstrating excellent thermal quenching property. Furthermore, the temperature sensing performance was evaluated by FIR technique according to the differential decreasing trend of Dy3+ and Sm3+ emission intensity with increasing temperature. Finally, we also certified the applicability of NaYTiO4:Dy3+,Sm3+ phosphors in white LEDs for indoor health lighting. These results indicate that NaYTiO4:Dy3+,Sm3+ multifunctional phosphors are promising dual functional luminescent platforms that can be used for non-contact optical thermometers and white LED device applications.

Dual-functional application of Ca2Ta2O7:Bi3+/Eu3+ phosphors in multicolor tunable optical thermometry and WLED

A series of Bi3+/Eu3+ co-doped Ca2Ta2O7 (CTO:Bi3+/Eu3+) phosphors were prepared by high-temperature solid-state method for dual-emission center optical thermometers and white light-emitting diode (WLED) device. By modulating the doping ratio of Bi3+/Eu3+ and utilizing the energy transfer from Bi3+ to Eu3+, the tunable color emission ranging from green to reddish-orange was realized. The designed CTO:0.04Bi3+/Eu3+ optical thermometers exhibit significant thermochromism, superior stability, and repeatability, with maximum sensitivities of Sa = 0.055 K-1 (at 510 K) and Sr = 1.298% K-1 (at 480 K) within the temperature range of 300-510 K, owing to the different thermal quenching behaviors between Bi3+ and Eu3+ ions. These features indicate the potential application prospects of the prepared samples in visualized thermometer or high-temperature safety marking. Furthermore, leveraging the excellent zero-thermal-quenching performance, outstanding acid/alkali resistance, and color stability of CTO:0.04Bi3+/0.16Eu3+ phosphor, a WLED device with a high Ra value of 95.3 has been realized through its combination with commercially available blue and green phosphors, thereby demonstrating the potential application of CTO:0.04Bi3+/0.16Eu3+ in near-UV pumped WLED devices.

Sb3+/Sm3+ Codoped Cs2NaScCl6 All-Inorganic Double Perovskite: Blue Emission of Self-Trapped Excitons and Red-Emission via Energy Transfer

The lead-free halide perovskites possess nontoxicity and excellent chemical stability, whereas relatively weak luminescence intensity limits their potential in practical applications. Therefore, strengthening the luminescence intensity and expanding application fields are urgent tasks for the development of lead-free halide perovskites. In this paper, antimony-doped Cs2NaScCl6 crystals synthesized by a solvothermal method emit bright, deep blue photoluminescence at 447 nm. The photoluminescence (PL), photoluminescence excitation (PLE), and absorption spectra demonstrate that Sb3+ doping effectively activate the intrinsic "dark self-trapped exciton (STE)," leading to an impressive photoluminescence quantum yield (PLQY) value of 78.31% for 1% Sb3+ doping. Furthermore, the luminescence intensity remains above 92% compared with the fresh sample without secondary phases detected even after 90 days under environmental conditions. To expand the emission spectra, rare-earth Sm3+ is further incorporated into Cs2NaScCl6:1% Sb3+ crystals. The results show that Sb ions not only enhance intrinsic STE luminescence but also serve as sensitizers to boost the red-light emission of Sm3+, leading to a significant 500-fold increase in red emission intensity. Finally, the PLQY reaches a stunning 86.78%. These findings provide valuable insights in the design of Sb ion-doped lead-free double perovskites, broadening the application fields in various optoelectronic devices.

Ce3+-Activated SrLu2Al3ScSiO12 Cyan-Green-Emitting Garnet-Structured Inorganic Phosphor Materials toward Application in Blue-Chip-Based Phosphor-Converted Solid-State White Lighting

Phosphor-converted white-light-emitting diodes (WLEDs) with superhigh color rendering index (CRI) are the ongoing pursuit of next-generation solid-state lighting. One of the most important challenges is the limited improvement in CRI on account of the absence of a cyan component in the typical commercial combination. Here, a bright broad-band cyan-green-emitting phosphor with cubic garnet structure, SrLu2Al3ScSiO12:Ce3+ (SLASSO:Ce3+), was successfully reported, which can compensate for the absence of cyan cavity in the 480-520 nm blue-green emission region. With 439 nm blue-light irradiation, the as-fabricated SLASSO:Ce3+ phosphor yields a broad-band cyan-green emission with the maximum emission peak positioned at 525 nm and an appropriate full width at half-maximum (fwhm) of 111 nm, capable of providing more cyan emission component without sacrificing green emission. Meanwhile, the optimal SLASSO:2%Ce3+ phosphor features CIE color coordinates of (0.3254, 0.5470) with cyan-green hue, along with a high internal quantum efficiency of up to 93%. Additionally, thermal stability measurements at different temperatures reveal that the luminescence emission intensity of the proposed phosphor retains 44% of its original integral emission intensity at 423 K with respect to room temperature, while also demonstrating an excellent color stability (ΔE = 5.4 × 10-3). This work shows that the highly efficient SLASSO:Ce3+ garnet phosphor can be utilized as a potential cyan-green-emitting phosphor for filling the cyan gap, resulting in the construction of a high-quality warm WLED with high CRI for "human-centric" sunlight-like full-spectrum solid-state illumination.

Color-tunable emissions realized by Tb3+ to Eu3+ energy transfer in ZnGdB5O10 under near-UV excitation

Photoluminescent (PL) energy transfer (ET) between two typical rare earth activators Tb3+ and Eu3+ is utilized to achieve color-tunable emission and the color range is apparently dependent on the ET efficiency. In the target host ZnGdB5O10 (ZGBO), the relatively low symmetric coordination environment of the rare earth cation not only suppresses the parity-forbidden law of the 4f-4f transitions of Tb3+ in the near-UV region, but also enhances the internal quantum efficiency (IQE), where the optimal IQE is 65.61% for ZGBO:0.8Tb3+. Moreover, its ET to Eu3+ is highly efficient, i.e. 94.71% in ZGBO:0.8Tb3+,0.10Eu3+, which eventually leads to a wide range of color-tunable emissions from green (0.2915, 0.5915) to red (0.6207, 0.3731). The systematic PL spectral study on Tb3+/Eu3+ singly doped and co-doped phosphors suggests that the ET mechanism takes place through the electric dipole-dipole interaction according to the Inokuti-Hirayama (I-H) model. Additionally, the in situ high temperature PL spectra indicate the very high thermal stability of ZnGd0.19Tb0.8Eu0.01B5O10, indicating that it can be a potential candidate for near-UV light emitting diode-pumped phosphors.

Facile and cost-effective technique to control europium oxidation states in glassy fluorophosphate matrices with tunable photoluminescence

Inorganic fluorophosphate glasses doped with Eu[Formula: see text]/Eu[Formula: see text] are potential candidates for phosphors for commercial white LEDs. This report presents a fast, inexpensive and effective method of controlling the relative concentrations of Eu[Formula: see text]/Eu[Formula: see text] photoluminescent centers in these glasses. The technique consists of a fast quenching of the melt of initial reagents under appropriate conditions. Eu[Formula: see text]/Eu[Formula: see text] ratio was controlled by carrying out the melting under a reducing atmosphere at a temperature between 1000 and 1200 [Formula: see text]C for periods of 5 to 15 minutes. The reducing atmosphere was provided by a 'double crucible' technique and did not require special gas lines during the synthesis. The samples were studied by several complementary experimental methods (X-ray diffractometry-XRD, X-ray photoelectron spectroscopy-XPS, photoluminescence-PL-and photoluminescence excitation-PLE-spectroscopies as well as optical transmission spectroscopy). It was shown that the syntheses resulted in amorphous materials with different relative Eu[Formula: see text]/Eu[Formula: see text] concentration ratios, strongly dependent on the preparation conditions: the temperature and the time of melting in a reducing atmosphere. Moreover, changes in these ratios strongly affected the materials' PL and PLE spectra. Demonstration of reproducible smooth transition from amaranth to blue luminescence color, with white in between, was the most spectacular result of this work.

Thermal Quenching Mechanism of Metal-Metal Charge Transfer State Transition Luminescence Based on Double-Band-Gap Modulation

Bi³⁺-related metal-to-metal charge transfer (MMCT) transition phosphors are expected to become a new class of solid-state luminescent materials due to their unique broadband long-wavelength emission; however, the main obstacle to their application is the thermal quenching effect. In this study, one novel thermal quenching mechanism of Bi³⁺-MMCT transition luminescence is proposed by introducing electron-transfer potential energy (ΔE_T). Y_0.99V_1-xP_xO₄:0.01Bi³⁺ (YV_1-xP_xO₄:Bi³⁺) is used as the model; when the band gap of the activator Bi³⁺ increases from 3.44 to 3.76 eV and the band gap of the host YV_1-xP_xO₄ widens from 2.75 to 3.16 eV, the electron-transfer potential energy (ΔE_T) decreases and the thermal quenching activation energy (ΔE) increases, which result in the relative emission intensity increasing from 0.06 to 0.64 at 303-523 K. Guided by density functional calculations, the thermal quenching mechanism of the Bi³⁺-MMCT state transition luminescence is revealed by the double-band-gap modulation model of the activator ion and the matrix. This study improves the thermal quenching theory of different types of Bi³⁺ transition luminescence and offers one neo-theory guidance for the contriving and researching of high-quality luminescence materials.

Modulating A site compositions of europium(iii)-doped double-perovskite niobate phosphors

Eu3+-activated double-perovskite niobates of A2InNbO6 were synthesized with the modulation of their A site and the polydimethylsiloxane flexible light-emitting films based on the optimized phosphors were implemented for versatile applications.